Private Data IO v6 app installed and connected, but no Read from step in Workflow Builder

Hi everyone,

I'm building a private, read-only Data IO v6 extension in a developer/sandbox account and have hit a snag. The app installs, the connections show Active, and I can retrieve test records in Developer Console. But when I open a workflow and go to Add New Step > Apps, all I see is Browse Apps. There's no Read from step for my app. I last checked this on November 6.

I'm following the Data IO workflow test in the documentation, which shows choosing a Read from [app name] step:
https://developers.docusign.com/extension-apps/build-an-extension-app/test/functional-tests/data-io-workflow

For context, the app is private, version 1.0.0, and still in Draft. It's installed in the same sandbox account I'm using for Workflow Builder. It uses DataIO.Version6.DataInputOutput with the Version 6 GetTypeNames, GetTypeDefinitions, and SearchRecords actions only. Developer Console lists it as Data Read. The connection uses OAuth client_credentials against an HTTPS service with fictional data.

Both metadata actions succeed and return HTTP 200, and the buyer-only and complete joint-deal lookups show Succeeded with the correct records. The schema is a flat EvoDeal ConceptDeclaration identified by Id, with Term and Crud("Readable") decorators on the declaration and properties. It also passes an independent Concerto validation.

I've tried Reload Objects, watched the connection go from Processing back to Active, created a separate Shared connection, reloaded Workflow Builder, and tried a completely new manual-start workflow. Both the Developer Console connection and the separate Shared connection are Active. I also checked again more than two hours later, but the step was still missing.

This started when the schema had ten string fields. I later added a required Boolean field and confirmed that DocuSign could return true and false, but that didn't change the missing-step issue. A couple of later tests with incomplete contact details showed an execution error or no result, so I can't count those as successful tests. I'm not sure whether they're related.

I found this article, but that report describes a Google Drive integration with a similar empty Connected Apps list. The replies focus on Google Workspace policies, and my service doesn't use Google, so I don't think that fix applies here:
https://community.docusign.com/workflow-builder-172/google-drive-steps-in-workflow-builder-formerly-maestro-26737

Am I missing an account setting or sandbox entitlement, or does a private app need a different approval/status before its read step appears? If Draft apps should work, is there a registration check or diagnostic I can use to see what's preventing it from showing up?

Standard Support pointed me toward the developer community, so I'd appreciate any guidance. This is all fictional test data, and I haven't sent any envelopes. I'm happy to share a sanitized manifest or schema if that would help. Thanks!